1. Field of the Invention
The present invention relates to a method of detecting a connecting relation between a signal repeater and a switching device, and a communication system suitable for implementation of the detecting method.
2. Description of the Related Art
Networks have been configured using a method of switching time slots which are time-division-multiplexed on an optical signal, where an increased switching unit of a communication network associated with an increase in communication traffic results in requirements for a function of switching the unit of optical signals. This function is implemented using an optical cross-connect system (OXC) which is based on an optical switch.
FIG. 1 is a block diagram illustrating the configuration of an exemplary prior art optical cross-connect system. Here, a device which has a function of receiving a certain signal and delivering this signal after it has undergone processing is defined as a “signal repeater.” Signal repeaters for transmitting signals in directions opposite to each other are collectively managed and are defined as a “bidirectional signal repeater.” Also, when a bidirectional signal repeater repeats an optical signal, this repeater is called the “bidirectional optical signal repeater.”
Referring to FIG. 1, optical fibers are connected to ports 1131, 1132, respectively, for connection with another node. Optical signal repeaters 1110, 1120 are collectively managed as a bidirectional optical signal repeater. Ports 1105, 1132 and 1107, 1134 are output ports of bidirectional optical signal repeaters 1110, 1120, respectively, while ports 1106, 1131 and 1108, 1133 are input ports of bidirectional optical signal repeaters 1110, 1120, respectively. An optical signal applied to port 1131 is delivered to port 1105; an optical signal applied to port 1106 is delivered to port 1132; an optical signal applied to port 1133 is delivered to port 1107; and an optical signal applied to port 1108 is delivered to port 1134. In the following, a pair of an input port and an output port which are connected to the same device is defined as a “bidirectional port pair”. Ports 1105, 1106, and ports 1131, 132 are bidirectional port pairs, respectively. In FIG. 1, the bidirectional port pairs are designated by (1105, 1106) and (1132, 1132), respectively.
A bidirectional optical signal repeater comprises a 3R regenerative repeater (hereinafter called the “regenerator”) and an optical fiber. Port 1131 and regenerator 1111 are interconnected through an optical fiber, while regenerator 1111 and port 1105 are also interconnected through an optical fiber. Likewise, port 1106 and regenerator 1112 are interconnected through an optical fiber, while regenerator 1112 and port 1132 are also interconnected through an optical fiber. Regenerator 1111 is located immediately before a transmitted optical signal is applied to optical switch 1100 because regenerator 1111 regenerates the optical signal into a waveform suitable for digital transmission. Also, regenerator 1112 is located immediately after the output of optical switch 1100 because an optical signal, which has passed through optical switch 1100, is regenerated by regenerator 1112 into a waveform suitable for transmission of digital signal. Assume now that SONET signals (see Bellcore document, GR-253-CORE, Issue 2, “Synchronous Optical Network (SONET) Transport Systems: Common Generic Criteria,” published by Bellcore, 1995 for the format of the SONET signal) are used as a signal which is repeated with 3R regeneration, and as signals which are switched by optical switch 1100. In this scenario, a regenerator described in the foregoing Bellcore document may be used for purposes intended herein. Controller 1115 controls or manages regenerators 1111, 1112, while controller 1125 controls or manages regenerators 1121, 1122. Controllers 1115, 1125 have a function of reading/writing values from/into the overhead as a control/management function.
Optical switch 1100 comprises input ports 1101, 1103, 1142, and output ports 1102, 1104, 1141. Optical switch 1100 employed herein may be configured as shown in JP-5-207528-A by way of example.
FIG. 1 in JP-5-207528-A illustrates an optical switch which has input ports located on the left-hand side of the drawing, and output ports located on the right-hand side of the drawing. Likewise, in optical switch 1100, when the input ports and associated output ports are handled in combination, and those connected to optical signal repeaters are defined as bidirectional port pairs, the ports can be managed in units of bidirectional port pairs. In FIG. 1, ports 1101 and 1102, ports 1103 and 1104, and ports 1141 and 1142 form bidirectional port pairs, respectively. Controller 1109 is associated with optical switch 1100 for controlling the switching of optical switch 1100. Regenerators 1111, 1112, 1121, 1122 are connected to ports 1105, 1106, 1107, 1108 of optical switch 1100, respectively.
Some bidirectional optical repeater provides connections with another device in the same node in addition to the connection with optical fibers which constitute a transmission path. A router, represented by 1800, is connected to bidirectional optical repeater 1170, which comprises regenerators 1171, 1172, controller 1175, and ports 1173, 1174, 1181, 1182, through ports 1173, 1174. Other than this connection, bidirectional optical repeater 1170 is connected to optical switch 1100 through its ports 1181, 1182 and ports 1183, 1184 of optical switch 1100.
To build and manage a network, a network management system must be registered with information as to which bidirectional signal repeater is connected to ports of which optical switch, so that the network management system preserves the network topology.
Conventionally, however, manual operations have been relied on to confirm which bidirectional signal repeater is connected to a bidirectional port pair of which optical switch. Specifically, connected cables are visually traced for visual confirmation of their connections. For example, in the configuration illustrated in FIG. 1, automated confirmation cannot be made as to which port of optical switch 1100 is connected to which port of bidirectional signal repeater 1105, so that a human operator must trace connected cables to confirm which port is connected to which port.
When connections are visually confirmed to register the connectivity and network topology in the network management system, human errors, if any, would result in erroneous registration and possible network faults.
In particularly, when a network is re-started immediately after installation or replacement of a certain device, or due to a fault, the connecting relation must be registered again in the network management system, in which case the network topology can be erroneously registered due to a human error as mentioned above.
Also, an optical signal passes through an optical switch as it is, and, among bidirectional signal repeaters, assuming that there is spare bidirectional optical signal repeater 1120 to which spare optical fibers are connected, an optical signal can not be applied from port 1133, because repeater 1120 is reserved as a spare, resulting in no signal flowing through a link between port 1107 and port 1103. The absence of signal between port 1107 and port 1103 inhibits the operator from managing the presence or absence of a fault on the link between bidirectional optical signal repeater 1120 and optical switch 1100. Therefore, the main signal must be switched without confirming that the optical link has not failed. If the main signal is switched for using the link between bidirectional signal repeater 1120 and optical switch 1100 in spite of a fault thereon, a longer time will be taken to recover from the fault because of surplus switching which cannot be recovered even if the link is recovered from the fault.